1. Field of the Invention
This invention relates to a hot rolling method for avoiding edge build-up and edge drop of rolled strips or plates by preventing local wear of work rolls of rolling mills such as four or six high mills simultaneously controlling shapes of steel strips or plates by crown-controlling.
2. Description of the Prior Art
Recently, there has been an increasing need to improve the accuracy in thickness of steel strips or plates rolled by rolling mills in order to improve the yield rate of the steel. To meet this need, various crown-controlling methods have been proposed. Among them, a taper end roll rolling method is effective to prevent edge drops with the aid of particular geometrical shapes of work rolls, (for example, as disclosed in Japanese patent application Publication No. 20,081/81).
In this case, the effect of crown-controlling tends to decrease with change in width of steel strips or plates. To avoid this, a work roll shift method is effective for the crown-controlling, (as disclosed in Japanese patent application Publication No. 151,552/78).
In hot finish rolling, as the number of rolled strips having the same width increases, work rolls 1 progressively wear to form tracks or traces 2 for strips or plates, whose edge portions 2b usually wear deeper than in center portions 2a as shown in FIG. 1. As a result, the rolled strip 3 has a sectional profile including at its edges irregular protrusions or ridges p and p' which are referred to as "edge build up" as shown in FIG. 2. It is clearly evident that such an edge built-up causes the greatest difficulty for crown-controlling of strips and roll-change-free rolling which is a rolling with a pair of work rolls over a wide range of sizes of strips or plates to be rolled without changing the rolls. The same holds true in the above crown-controlling by the use of the taper end rolls.